Endothelial permeability increases with organ injury in a number of disease states. This disturbance of vascular barrier function results in local fluid accumulation, tissue edema, and organ dysfunction. Although pathologic increases in vascular permeability are often associated with polymorphonuclear leukocyte (PMN) accumulation and activation, their role in modulating endothelial permeability is unclear. We developed a human endothelial cell model to answer basic questions regarding PMN-mediated changes in endothelial permeability. Preliminary data reveal that PM release a small (molecular weight less than 10 kD), heat-stable factor (or family of factors) that decreases endothelial permeability; we have termed this factor neutrophil-derived endothelial permeability factor (NEPF). We hypothesize that PMN release a soluble compound which decreases endothelial permeability, thereby increasing endothelial barrier function. Three specific aims are directed at testing this hypothesis. First, utilizing physical methods , we will characterize and elucidate the structural nature of NEPF. Seconds we will examine conditions in which PMN release NEPF and characterize NEPF pathways of action on endothelial cells. And third, we will examine the impact of a panel of biologically relevant inflammatory mediators and conditions on NEPF action on endothelial cells. The experiments outlined in this proposal will yield insight into the regulation of endothelial permeability during disease states and may provide the basis for the development of novel therapeutics for disorders of vascular perm. The proposed research will be performed in a center that is specifically focused on questions related to the biochemical nature of inflammation- related organ injury. The candidate is an accomplished clinician with a strong interest in basic science research and an experienced investigator in whole animal research. The candidate's immediate career goal is to attain proficiency in methods required to investigate organ function at the cellular and biochemical level. The candidate's long term career goal is to establish and maintain a research program which produces insight into basic mechanisms related to clinical important disease.